Recently, the applicability of magnetic recording apparatuses such as magnetic disk devices, flexible disk devices and magnetic tape devices has increased significantly, and the importance thereof has also increased. Also, the recording density of magnetic recording media used for these devices has been increased significantly. With the introduction of an MR head and a PRML technology, surface recording density has improved still more significantly. In recent years, GMR heads and TMR heads have also been introduced, which further increase the surface recording density by about 1.5 times per year.
Accordingly, there is a demand to further increase the recording density of these magnetic recording media. Thus, it is required to increase a coercive force, a signal-to-noise ratio (SNR) and resolution of magnetic layers. In recent years, efforts have been made to increase surface recording density by increasing linear recording density and track density.
The most recent magnetic recording apparatus has track density of as high as 250 kTPI (Track Per Inch). As the track density increases, however, magnetic recording information between adjacent tracks begins interfering with each other, which may easily cause a problem that a magnetizing transition area of a border area becomes a noise source that decreases the SNR. The decrease in the SNR causes a decrease in a bit error rate, which is an obstacle to an improvement in recording density.
In order to increase surface recording density, it is necessary to provide reduced-sized recording bits on the magnetic recording medium, each recording bit having maximum possible saturation magnetization and maximum possible magnetic film thickness. There is a problem, however, that the reduced-sized recording bit has a small magnetizing minimum volume per 1 bit and recorded data may disappear due to magnetization reversal caused by heat fluctuation.
Since adjacent tracks are close to each other in a high track density configuration, a significantly precise track servo technique is necessary for a magnetic recording/reproducing apparatus. Also, information is recorded on a larger number of tracks and reproduced in a smaller number of tracks in order to avoid influence from adjacent tracks as much as possible. In this manner, however, although influence between the tracks can be controlled to the minimum, it is difficult to obtain a sufficient reproduction output and thus to provide a sufficient SNR.
In order to avoid the above heat fluctuation problem and to provide a sufficient SNR and sufficient output, an attempt has been made to form a concavo-convex configuration along the tracks on the surface of the recording medium so as to physically separate the recording tracks from one another to increase the track density. Such a technique is usually referred to as a discrete track method, and a magnetic recording medium manufactured by this discrete track method is referred to as a discrete track medium. An attempt has also been made to provide a so-called patterned medium that has further divided data areas in the same track.
There is known, as an example of the discrete track medium, a magnetic recording medium in which a magnetic layer is formed on a non-magnetic substrate with a concavo-convex pattern formed on the surface to form a physically-separated magnetic recording track and a servo signal pattern (see, for example, Patent Literature 1).
The disclosed magnetic recording medium includes a ferromagnetic layer formed on the surface of a substrate with plural concavo-convex configurations via a soft magnetic layer, a protective film being formed on the surface of the ferromagnetic layer. The magnetic recording medium has, in its convex area, a magnetic recording area which is physically separated from the surrounding areas.
According to the magnetic recording medium, since formation of a magnetic wall in the soft magnetic layer can be avoided, influence of the heat fluctuation hardly occurs, and there is no interference between adjacent signals. Consequently, a high-density magnetic recording medium with less noise can be provided.
The discrete track method includes a method of forming tracks after a magnetic recording medium constituted of several thin film layers is formed, and a method of preliminarily forming a concavo-convex pattern directly on a substrate surface or on the thin film layer for track formation, and then forming a thin magnetic recording medium film (see, for example, Patent Documents 2 and 3).
Of these, the former method is referred to as a magnetic layer processing type. However, physical processing is conducted for the surface of a formed medium in this method. Therefore, there are problems in that a medium is likely to be contaminated during a production step and a production method becomes very complicated. Meanwhile, the latter method is referred to as an embossing type. In this method, a medium is hardly to be contaminated during a production step. However, a concavo-convex shape formed on a substrate is transferred to a film formed thereon. Therefore, there are problems in that the float attitude and float height of a recording/reproducing head, which performs recording/reproducing while floating on a medium, become unstable.
As the method of forming an area between magnetic tracks of a discrete track medium, there is disclosed a method of irradiating with laser or injecting nitrogen ions and oxygen ions into a preliminarily formed magnetic layer so as to change magnetic characteristics of subjected area (see, for example, Patent Literatures 4 to 6).
In addition, there is disclosed a method in which a concavo-convex pattern is formed on the surface of a magnetic layer, a non-magnetic layer is formed to cover this surface, and then, this surface of this non-magnetic layer is smoothened by oblique ion beam etching or CMP (Chemical Mechanical Polishing) (see, for example, Patent Literature 7).